转载：http://blog.csdn.net/java04/article/details/51339535#android基础知识点总结
Android基础知识点总结
在学习了很长一段时间的Android基础内容，如果不做及时的复习，那么后面的项目学习起来可能就没那么顺利了，并且复习也是一件很愉快的事。古人有云：“学而时习之不亦说乎”，应该就是这个道理。
~本文大纲~
- Android基础知识点总结
- Day01
- 01Android系统中我们常用的4种数据存储方式
- 02获取手机内存空间大小
- 03XML文件的生成和解析
- GET新技能
- Day02
- SQLiteOpenHelper的基本用法
- 数据库事务
- Listview的简单优化
- day03
- day04
- day05
- day06
- day07
- day08
- day09
Day01
第一天主要学习的内容相对零散一点，但还是很重要的。
01、Android系统中我们常用的4种数据存储方式★★★★★
1. SharedPreferences存储数据 2. getFilesDir数据存储在手机上 3. Environment数据存储在SD卡上 4. SQLite数据库存储
1、SharedPreferences存储数据
保存数据
SharedPreferences config = getSharedPreferences("config", MODE_PRIVATE) boolean commit = config.edit().putString("Hsia", mContent).commit() if (commit) { Toast.makeText(getApplicationContext(), "数据保存成功！", Toast.LENGTH_SHORT).show() mEtContent.setText("") }
取回数据
String getConfig = getSharedPreferences("config", MODE_PRIVATE).getString("Hsia", "") if (!("".equals(getConfig))) { Toast.makeText(getApplicationContext(), "数据取回成功！", Toast.LENGTH_SHORT).show() mEtContent.setText(getConfig) }
2、getFilesDir数据存储在手机上
/** * 获取已保存的用户信息 * @param context * @return */ private String getConfigFile(Context context) { try { BufferedReader br = new BufferedReader(new FileReader(new File(context.getFilesDir(), FILENAME))); String data = br.readLine(); br.close(); return data; } catch (Exception e) { e.printStackTrace(); } return null; } /** * 保存用户信息到手机上 * @param context * @param mContent * @return */ private boolean SaveConfig(Context context, String mContent) { if (mContent != null) { File file = new File(context.getFilesDir(),FILENAME); try { BufferedWriter bw = new BufferedWriter(new FileWriter(file)); bw.write(mContent); bw.newLine(); bw.close(); return true; } catch (IOException e) { e.printStackTrace(); return false; } }else{ return false; } }
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3、Environment数据存储在SD卡上
/** * 从sd卡中取出数据 * @return */ private String SDGetConfig() { String state = Environment.getExternalStorageState(); if (Environment.MEDIA_MOUNTED.equals(state)) { try { FileReader fr = new FileReader(new File(Environment.getExternalStorageDirectory() + SDDownload, FILENAME)); int len = 0; char[] chs = new char[1024]; String data = ""; while((len = fr.read(chs))!=-1){ data = new String(chs,0,len); } fr.close(); return data; } catch (Exception e) { e.printStackTrace(); } } return null; } /** * 保存数据到sd卡中 * @param mContent * @return */ private boolean SDSaveConfig(String mContent) { String state = Environment.getExternalStorageState(); if (!(Environment.MEDIA_MOUNTED.equals(state))) { return false; }else{ try { FileWriter fw = new FileWriter(new File(Environment.getExternalStorageDirectory() + SDDownload, FILENAME)); fw.write(mContent); fw.close(); return true; } catch (Exception e) { e.printStackTrace(); } } return false; }
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- SharedPreferences存储数据，会在当前包名下，生成一个“shared_prefs”文件夹，配置文件放在该目录下。
- getFilesDir存储数据，会在当前包名下，生成一个“files”文件夹，配置文件放在该目录下。
- Environment存储数据，获取到SD卡根目录，文件默认会存放在SD卡根目录中。
4、SQLite数据库存储（相对知识点较多暂时不做演示）
02、获取手机内存空间大小★★★
由于获取手机空间大小实际开发中使用较少，并且相对简单，就不做代码测试了，主要就用到Environment（获取SD卡空间）和getFilesDir（获取手机空间）。
关键代码
File storageDirectory = Environment.getExternalStorageDirectory()long totalSpace = storageDirectory.getTotalSpace()long usableSpace = storageDirectory.getUsableSpace()
File filesDir = getFilesDir();long totalSpace = filesDir.getTotalSpace();long usableSpace = filesDir.getUsableSpace();String totalSpaceStr = Formatter.formatFileSize(this, totalSpace);String usableSpaceStr = Formatter.formatFileSize(this, usableSpace);
03、XML文件的生成和解析★★★
/** * 生成XML文件的方法 * @return */ private boolean MakeXML() { XmlSerializer xmlSerializer = Xml.newSerializer(); File file = new File(getFilesDir(), "makeXML.xml"); try { FileOutputStream fos = new FileOutputStream(file); xmlSerializer.setOutput(fos,"utf-8"); xmlSerializer.startDocument("utf-8",true); xmlSerializer.startTag(null,"Message"); for (int i = 0; i < 5; i++) { xmlSerializer.startTag(null,"sms"); xmlSerializer.startTag(null,"address"); xmlSerializer.text("15855225588"); xmlSerializer.endTag(null,"address"); xmlSerializer.startTag(null,"name"); xmlSerializer.text("Hsia"); xmlSerializer.endTag(null,"name"); xmlSerializer.startTag(null,"body"); xmlSerializer.text("Hello!!!!"); xmlSerializer.endTag(null,"body"); xmlSerializer.endTag(null,"sms"); } xmlSerializer.endTag(null,"Message"); xmlSerializer.endDocument(); return true; } catch (Exception e) { e.printStackTrace(); } return false; }
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private List<Weather> GetResolveXML(File file) { XmlPullParser parser = Xml.newPullParser(); FileInputStream fis = null; List<Weather> list = null; Weather weather = null; try { fis = new FileInputStream(file); parser.setInput(fis,"utf-8"); int type = parser.next(); while(type!=XmlPullParser.END_DOCUMENT){ if (type==XmlPullParser.START_TAG) { list = new ArrayList<>(); if ("weather".equals(parser.getName())) { weather = new Weather(); }else if ("city".equals(parser.getName())) { String id = parser.nextText(); weather.setId(id); }else if ("name".equals(parser.getName())) { String name = parser.nextText(); weather.setName(name); }else if ("pm".equals(parser.getName())) { String pm = parser.nextText(); weather.setPm(pm); }else if ("wind".equals(parser.getName())) { String wind = parser.nextText(); weather.setWind(wind); }else if ("temp".equals(parser.getName())) { String temp = parser.nextText(); weather.setTemp(temp); } } type = parser.next(); list.add(weather); } fis.close(); return list; } catch (Exception e) { e.printStackTrace(); } return null; }
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GET新技能
Day02
主要学习Android-SQLite和ListView控件的使用
SQLiteOpenHelper的基本用法
1、SQLiteOpenHelper一般就是写一个类，继承SQLiteOpenHelper来创建一个数据库。
public class MyOpenHelp extends SQLiteOpenHelper { public MyOpenHelp(Context context) { super(context, "person.db", null, 1); } /** * Called when the database is created for the first time * 当 数据第一次创建的时候调用 * 该方法适合做 表结构的初始化 */ @Override public void onCreate(SQLiteDatabase db) { System.out.println("oncreate"); db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20),phone varchar(20))"); } /** * 当数据库需要升级的时候调用 * 该方法适合做 表结构修改 * */ @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { System.out.println("onUpgrade"); }}
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2、新建一个针对数据库的操作类
/** * Created by Hsia on 16/5/12. * E-mail: xiaweifeng@live.cn * //TODO:对数据操作的类 */public class PersonDao { private final MyOpenHelp help; public PersonDao(Context context) { help = new MyOpenHelp(context); } /** * 插入数据到数据库的方法 * @param name * @param phone * @return */ public boolean add(String name,String phone){ SQLiteDatabase db = help.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("name",name); values.put("phone",phone); long l = db.insert("info", null, values); db.close(); if (l == -1){ return false; }else{ return true; } } /** * 数据库的删除方法 * @param name * @return */ public int del(String name){ SQLiteDatabase db = help.getWritableDatabase(); int info = db.delete("info", "name = ?", new String[]{name}); return info; } /** * 更改数据库，通过名字更改号码 * @param name * @param phone * @return */ public int update(String name,String phone){ SQLiteDatabase db = help.getWritableDatabase(); ContentValues values = new ContentValues(); values.put("phone",phone); int info = db.update("info", values, "name = ?", new String[]{name}); return info; } public String find(){ SQLiteDatabase db = help.getWritableDatabase(); /** * table 表名 * columns 查询的列 具体查询的是哪一列 * selection 根据什么条件去 * selectionArgs */ Cursor cursor = db.query("info", null, null, null, null, null, null); String name = ""; String phone = ""; while (cursor.moveToNext()){ name = cursor.getString(0); phone = cursor.getString(1); } db.close(); if (TextUtils.isEmpty(name)||TextUtils.isEmpty(phone)) { return null; }else { return name +","+ phone; } }}
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3、对数据库进行增删改查
public void onClick(View view) { switch (view.getId()) { case R.id.btn_add: boolean zhansan = dao.add("zhansan", "13888888") if (zhansan){ Toast.makeText(this, "数据添加成功", Toast.LENGTH_SHORT).show() }else{ Toast.makeText(this, "数据插入失败", Toast.LENGTH_SHORT).show() } break case R.id.btn_del: int del = dao.del("zhansan") if (del >1) { Toast.makeText(this, "删除了" + del + "行", Toast.LENGTH_SHORT).show() }else { Toast.makeText(this, "数据库已经没有数据了", Toast.LENGTH_SHORT).show() } break case R.id.btn_update: int update = dao.update("zhansan", "1377") Toast.makeText(this, "更改了" + update + "行数据", Toast.LENGTH_SHORT).show() break case R.id.btn_find: String find = dao.find() if (find != null) { String[] split = find.split(",") String name = split[0] String phone = split[1] Toast.makeText(this, "查询结果:" + name + "," + phone, Toast.LENGTH_SHORT).show() }else{ Toast.makeText(this, "数据库中，没有数据了", Toast.LENGTH_SHORT).show() } break } }
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数据库事务
即同一组操作要么同时成功，要么同时失败.
public void click(View view){ db.beginTransaction(); try { db.execSQL("update account set money = money - 100 where name = ?", new Object[] { "张三" }); int i = 1 / 0; db.execSQL("update account set money = money + 100 where name = ?", new Object[] { "李四" }); db.setTransactionSuccessful(); } catch (Exception e){ Toast.makeText(getApplicationContext(), "数据库操作失败，数据已回滚到上个版本", Toast.LENGTH_SHORT).show(); } finally { db.endTransaction(); }
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Listview的简单优化
if (convertView == null) { tv = new TextView(getApplicationContext()); System.out.println("创建新的view对象--"+position); }else { tv = (TextView) convertView; System.out.println("复用历史缓存对象--"+position); }
复用历史缓存对象
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ListView listView = (ListView) findViewById(R.id.lv); MyAdapter myAdapter = new MyAdapter(); listView.setAdapter(myAdapter); } class MyAdapter extends BaseAdapter{ @Override public int getCount() { return Integer.MAX_VALUE; } @Override public Object getItem(int position) { return null; } @Override public long getItemId(int position) { return 0; } @Override public View getView(int position, View convertView, ViewGroup parent) { View view = null; if (convertView == null) { view = View.inflate(getApplicationContext(), R.layout.item, null); System.out.println("Hsia:创建listview对象"+position); }else { view = convertView; System.out.println("Hsia:复用listview历史对象"+position); } return view; } }
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day03
主要学习Android下访问网络的操作，涉及到Handle消息机制的处理
消息机制的写法
(1)在主线程创建一个Handler 对象 (2)重写Handler的HandleMessage方法 (3)拿着handler 去子线程发送一条消息 (4)发送完消息后 handleMessage方法就会执行
网络图片查看器
public class MainActivity extends AppCompatActivity { private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { int what = msg.what; switch (what){ case 1: Toast.makeText(MainActivity.this, "访问网络失败", Toast.LENGTH_SHORT).show(); break; default: break; } super.handleMessage(msg); final Bitmap bitmap = (Bitmap) msg.obj; Toast.makeText(MainActivity.this, "3秒后执行", Toast.LENGTH_SHORT).show(); handler.postDelayed(new Runnable() { @Override public void run() { iv.setImageBitmap(bitmap); } },3000); } }; private ImageView iv; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); iv = (ImageView) findViewById(R.id.iv); } public void look(View view){ lookPng(); } private void lookPng() { new Thread(){ @Override public void run() { String path = "https://img.alicdn.com/tps/i1/TB1h3IXGFXXXXXsXFXXDANtWXXX-175-175.png_.webp"; HttpURLConnection conn = null; try { conn = (HttpURLConnection) new URL(path).openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); int code = conn.getResponseCode(); if (code == 200) { InputStream inputStream = conn.getInputStream(); Bitmap bitmap = BitmapFactory.decodeStream(inputStream); Message msg = Message.obtain(); msg.obj = bitmap; handler.sendMessage(msg); }else{ handler.sendEmptyMessage(1); } } catch (IOException e) { e.printStackTrace(); } } }.start(); }}
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备注：关于访问网络的内容暂时就写这么多了，后面什么Httpclient，由于谷歌在Android5.0的时候已经废弃了，所以，不做赘述。
day04
Android学习从零单排之Activity
day05
Android学习从零单排之BroadcastReceiver
day06
Android学习从零单排之Service
day07
Android学习从零单排之ContentProvider
day08
Android学习从零单排之Androidmultimedia（多媒体）
day09
Android学习从零单排之Fragment
由于学习时间有限，以上部分，就不做总结了，请参考链接。
关于作者
- 个人网站：北京互联科技
- Email：xiaweifeng@live.cn
- 项目地址:https://github.com/swordman20/AndroidBaseContent.git
转载：http://blog.csdn.net/java04/article/details/51339535#android基础知识点总结
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